1. Technical Field
This invention relates to studded footwear such as sports shoes, for example football boots track and field shoes, golf shoes, and footwear for other sports. The term “football” is intended to encompass all sports known as football, such as soccer, rugby and American and Australian football.
2. Discussion of Known Art
The studs of the present invention are intended to provide traction, having a ground-engaging part of a type suited to the sport involved. Thus, studs for football tend to have relatively sharp ground-piercing spikes, while those for golf shoes currently have several relatively soft and blunt ground-gripping or turf-engaging cleats. The studs are detachably fastened to the sole of the article of footwear, by a screw-threaded spigot on the stud engaging in a correspondingly threaded socket in a receptacle melded in, or otherwise secured to, the shoe sole.
The screw-threaded connection must be designed to ensure that the stud remains in place, even when high torque or traction forces are applied, and in particular that the stud does not unscrew accidentally. Known studs have either a single start thread or a multi-start thread. A single start thread is the simplest thread form and provides a greater resistance to unscrewing than a multi-start thread. It also provides a strong connection over the several turns of the thread on the spigot and socket. However, because of the number of turns needed to attach and detach the stud, removal and replacement with a single start thread becomes a time-consuming operation. A multi-start thread has a steeper helix angle, which enables a spigot of any given length to be inserted into the socket with less rotation. Also, because a multi-start thread is deeper cut than a single start thread, the shear strength of the thread is greater, so that a shorter spigot can be used.
Whether a single start or multi-start thread is used, the studs and sockets also typically incorporate a locking ratchet to prevent accidental unscrewing of the studs. Typically, the stud and socket each have a set of teeth which inter-engage as the stud is inserted into the socket. The arrangement of the teeth allows the stud to be in any one of a number of positions relative to the socket when it is fully inserted.
The screw threads and locking ratchets described are quite adequate where the final rotational orientation of the stud relative to the sole is not significant. In fact, currently most studs are circular or otherwise rotationally symmetrical, and their final rotational or angular orientation relative to the shoe sole is not relevant.
However, in some sports where the forces on the studs are relatively high and of a particular type, such as lateral forces or forces due to rapid forward acceleration of the wearer of the shoe, studs which are specifically oriented can be more effective. (The term “specifically-oriented stud” will be used herein to include studs which are non-rotationally symmetrical, or studs which are rotationally symmetrical but whose final orientation relative to the shoe sole is significant.) A specifically-oriented stud must be oriented very precisely relative to the shoe sole to ensure that it functions in the desired manner. The known screw-threads and locking ratchets are unable to provide this precise orientation. For example, although a single start thread orients the stud at the start of its insertion, the multiple turns and the locking ratchet mean that its final position cannot be predicted. A multi-start thread of course provides a plurality of starting positions, and the locking ratchet a plurality of end positions.